1. Field of the Invention
This invention relates to a process for sterilizing loose material by means of sterilizing agents, such as superheated steam, which are positively mixed with the continuously agitated material with exclusion of air to heat the material to the sterilization temperature. The invention also relates to an apparatus for carrying out such a process, comprising a sterilization container in which an agitator is rotatably mounted to agitate the material to be sterilized and which is provided with means for discharging and introducing sterilizing agents.
2. Description of the Prior Art
It has become increasingly customary to sterilize loose materials such as flour, cocoa, feedstuffs, fillers for cosmetics and pharmaceuticals and mould cultures, so that completely new fields of application have opened up for sterilisation. In particular, sterilisation must be adapted to high throughput rates for such bulk goods.
Various continuously operating apparatus for sterilizing loose material are already known which contain stationary or movable baffles and inserts to ensure that the product which is being treated cannot leave the apparatus until it has been in it for the minimum length of time required for sterilisation. In spite of elaborate constructional measures, however, so-called short circuits cannot be prevented in practice, that is to say portions of the products being treated are liable to pass too rapidly through the apparatus so that they do not stay in it for the minimum time prescribed for sterilisation. If portions of the product are left unsterilized, the whole quantity of the product is, of course, unsterile since the non-sterilized portions contaminate the remainder. It is also difficult to empty such apparatus completely and clean them.
For batchwise sterilisation of loose material using steam or gas as the sterilizing agent, it is known to loosen up the material vigorously and agitate it so as to fluidize it and at the same time add the sterilizing agent and thereafter discharge the sterilizing agent from the sterilized material at subatmospheric pressure while the material continues to be vigorously agitated and loosened up (German Offenlegungsschrift 1,642,087). To ensure complete sterilisation, the material must be kept at the sterilisation temperature for a given time which varies according to the temperature. The higher the sterilisation temperature employed, the shorter is the necessary sterilisation time. Since, however, there is a limit to the sterilisation temperature which can be employed, the material must be kept in the sterilisation zone for a comparatively long period and at the same time thoroughly loosened up and agitated. Due to its comparatively long residence time in the structurally complicated dynamic sterilizer, the material is then liable to suffer mechanical damage.